Optical receiver, optical transmitter and optical transceiver

ABSTRACT

An optical receiver includes a first light receiving element to convert an optical signal to an electric signal and to output the electric signal from one end. A light receiving element row is connected to the other end of the first light receiving element to supply electric power to the first light receiving element. The light receiving element row includes a plurality of second light receiving elements connected in series.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Applications No. 2003-154910 and No.2003-154934, filed on May 30, 2003, the entire contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical receiver, opticaltransmitter and optical transceiver.

2. Related Background Art

FIG. 5 is a circuit diagram of a conventional optical receiver. Theconventional optical receiver includes a light receiving element 2, anamplifier circuit 4 and a capacitor 8. The light receiving element 2receives an optical signal, and generates an optical current. Theamplifier circuit 4 amplifies the optical current generated in the lightreceiving element 2, and outputs the amplified optical current. Thecapacitor 8 is provided to remove noise from a power supply Vcc, whichsupplies a voltage to the amplifier circuit 4.

In the conventional optical receiver, the power supply Vcc, whichsupplies the voltage to the amplifier circuit 4, is connected to thelight receiving element 2 as well. Therefore, the power supply Vcc notonly supplies the voltage to the amplifier circuit 4, but also applies areverse bias voltage to the light receiving element 2.

FIG. 19 is a schematic diagram of a conventional optical transceiver.The optical transceiver includes a light emitting element 1 and a lightreceiving element 3 for signal transmission. The light emitting element1 and the light receiving element 3 can be mounted on a singlelight-transmitting package.

FIG. 20 is a schematic diagram of another conventional opticaltransceiver. A light emitting element 1 is disposed on a light receivingelement 3. As a result, the optical transceiver is small-sized, and thelight emitting element 1 and the light receiving element 3 canrespectively transmit and receive signals via the same optical fiber.

As the reverse bias voltage applied to the light receiving element 2 inthe conventional optical receiver is made greater, the capacitance andresistance of the light receiving element 2 for high frequency signalsbecome lower. The greater the reverse bias voltage becomes, therefore,the more the optical receiver suits high-rate communication.

In the conventional optical receiver, however, it is impossible to applyto the light receiving element 2 a voltage which is larger than thepower supply voltage Vcc supplied to the amplifier circuit 4. In otherwords, there is a problem that the transmission rate of the opticalreceiver is limited by a value of the power supply voltage Vcc.

The capacitance of the light receiving element 2 can be reduced byreducing the area of the light receiving element 2. However, reducingthe area of the light receiving element 2 causes a problem that theoptical current supplied from the light receiving element 2 is reducedand coupling to the optical fiber, which transmits an optical signal,becomes difficult.

Furthermore, in the conventional optical transceiver shown in FIGS. 19and 20, the light emitting element 1 emits light in response to theforward bias voltage supplied from the power supply, and the lightreceiving element 3 converts an optical signal to an electric signal inresponse to the reverse bias voltage supplied from the power supply.Therefore, the light emitting element 1 depends upon the power supplyvoltage, and the light emitting element 1 cannot be supplied with avoltage exceeding the power supply voltage. The light receiving element3 also depends upon the power supply voltage, and the light receivingelement 3 cannot be supplied with a voltage exceeding the power supplyvoltage. As a result, the rate of the optical signal, which the lightreceiving element 3 can receive, is limited by the power supply voltage.

Documents related with the Related Background Art described above areJapanese Patent Laid-Open No. H6-216738 and No. H4-113713.

SUMMARY OF THE INVENTION

An optical receiver comprises a first light receiving element to convertan optical signal to an electric signal and to output the electricsignal from one end thereof; and a light receiving element row connectedto the other of the ends of said first light receiving element to supplyelectric power to said first light receiving element, said lightreceiving element row including a plurality of second light receivingelements connected in series.

An optical transmitter comprises a light emitting element of surfacelight emission type to convert an electric signal to an optical signaland transmit the optical signal; and a light receiving element rowexposed to light emitted from said light emitting element to generateelectric power, said light receiving element row including a pluralityof light receiving elements connected in series, wherein light emittedfrom a top surface of said light emitting element is used as an opticalsignal, and said light receiving element row is exposed to light emittedfrom a rear surface of said light emitting element.

An optical transceiver comprises a light emitting element to convert anelectric signal to an optical signal and transmit the optical signal; afirst light receiving element to receive the optical signal and convertthe optical signal to an electric signal, then output the electricsignal; and a light receiving element row including a plurality ofsecond light receiving elements connected in series between said lightemitting element and said first light receiving element, said lightreceiving element row being exposed to light emitted from said lightemitting element, and thereby said light receiving element row supplyingelectric power to said first light receiving element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a circuit diagram of an optical receiver according to a firstembodiment of the present invention;

FIG. 1B is a circuit diagram of an optical receiver according to asecond embodiment of the present invention;

FIG. 2 is a schematic diagram showing an optical receiver 100 a as afirst variant of an optical receiver 100;

FIG. 3 is a schematic diagram showing an optical receiver 100 b as asecond variant of the optical receiver 100;

FIG. 4 is a circuit diagram of an optical receiver 200 according to athird embodiment of the present invention;

FIG. 5 is a circuit diagram of a conventional optical receiver;

FIG. 6 is a sectional view of an optical transmitter 300 according to afourth embodiment of the present invention;

FIG. 7 is a top view of a light emitting element 130;

FIG. 8 is a bottom view of the light emitting element 130;

FIG. 9 is an equivalent circuit diagram of the optical transmitter 300;

FIG. 10 is an equivalent circuit diagram of the optical transmitter 300;

FIG. 11 is a sectional view of an optical transmitter 400 according to afifth embodiment of the present invention;

FIG. 12 is a top view of an optical transmission chip 130 in an opticaltransmitter 400;

FIG. 13 is a bottom view of the optical transmission chip 130 in theoptical transmitter 400;

FIG. 14 is a sectional view of an optical transceiver 500 according to asixth embodiment of the present invention;

FIG. 15 is a sectional view of an optical transceiver 600 according to aseventh embodiment of the present invention;

FIG. 16 is an equivalent circuit diagram of the optical transceiver 500or 600 shown in FIG. 14 or FIG. 15;

FIG. 17 is an equivalent circuit diagram of the optical transceiver 500or 600 shown in FIG. 14 or FIG. 15;

FIG. 18 is a sectional view of an optical transmitter 700 according toan eighth embodiment of the present invention;

FIG. 19 is a schematic diagram of a conventional optical transceiver;and

FIG. 20 is a schematic diagram of a conventional optical transceiver.

DETAILED DESCRIPTION OF THE INVENTION

Hereafter, embodiments of the present invention will be described withreference to the drawings. These embodiments do not restrict the presentinvention.

First, embodiments of an optical receiver according to the presentinvention will now be described. The embodiments of an optical receiveraccording to the present invention include a light receiving element rowformed of a plurality of light receiving elements connected in series.When the light receiving element row is exposed to light, the lightreceiving element row generates an optical voltage greater than a powersupply voltage. By applying the optical voltage to the light receivingelements, the optical receiver can cope with high-rate communication.

FIRST EMBODIMENT

FIG. 1A is a circuit diagram of an optical receiver 100 according to afirst embodiment of the present invention. The optical receiver 100includes light receiving elements 9, a light receiving element 20 and anamplifier circuit 40. A plurality of light receiving elements 9 areconnected in series and generate electric power, being exposed to lightP. A plurality of light receiving elements 9 connected in series areherein referred to as a light receiving element row 10. The lightreceiving element row 10 is connected on its cathode side to the ground,and connected on its anode side to a cathode of the light receivingelement 20. The light receiving element 20 is connected at its anode toan input terminal of the amplifier circuit 40. The light receivingelement 20 receives an optical signal S from optical fiber (not shown),and converts the optical signal S to an optical current (hereafter alsoreferred to as “electric signal”). The amplifier circuit 40 receiveselectric power from a power supply Vcc, and thereby amplifies theelectric signal output from the light receiving element 20. Afteramplifying the electric signal, the amplifier circuit 40 outputs theelectric signal via an output terminal OUT.

SECOND EMBODIMENT

FIG. 1B shows an optical receiver 101 according to a second embodimentof the present invention. The optical receiver 101 is different from theoptical receiver 100 in that the anode side of the light receivingelement row 10 is connected to the ground GND and the cathode side ofthe light receiving element row 10 is connected to the light receivingelement 20. In addition, the optical receiver 101 is different from theoptical receiver 100 in that the anode side of the light receivingelement 20 is connected to the light receiving element row 10 and thecathode side of the light receiving element 20 is connected to the inputterminal of the amplifier circuit 40.

Each of the light receiving elements 9 and the light receiving element20 is, for example, a photodiode or the like. The light receivingelements 9 may be different from each other in characteristics.Preferably, however, the light receiving elements 9 have the samecharacteristics. As a result, electric power generated by the lightreceiving element row 10 can be controlled by the number of the lightreceiving elements 9 connected in series. If a plurality of the lightreceiving elements 9 share the same characteristics, then the opticalreceiver 100 can be manufactured relatively easily. The characteristicsof a light receiving element referred to as herein include an elementsize, an efficiency of conversion from an optical signal to an opticalcurrent or optical voltage, and parasitic capacitance.

From the viewpoint that the optical receiver 100 can be manufacturedeasily, each of the light receiving elements 9 may be the same incharacteristics as the light receiving element 20. However, thecharacteristics of the light receiving elements 9 may be made differentfrom those of the light receiving element 20. For example, in the casewhere the same reverse bias voltage is applied to each of the lightreceiving elements 9 and the light receiving element 20, the capacitanceand the resistance of each of the light receiving elements 9 for highfrequency signals may be greater than those of the light receivingelement 20. In the case where both the light receiving elements 9 andthe light receiving element 20 are exposed to an optical signal S asshown in FIG. 3, the light receiving element 20 can receive the opticalsignal S as a signal, whereas the light receiving elements 9 can receivethe optical signal S as a continuous light and can continuously generatepower.

According to the first and second embodiments, the number of the lightreceiving elements 9 is adjusted according to intensity of light P thatthe light receiving element row 10 is exposed to. As a result, theoutput voltage of the light receiving element row 10 can become greaterthan the power supply voltage Vcc. When the output voltage of the lightreceiving element row 10 exceeds the power supply voltage Vcc, since thereverse bias voltage applied to the light receiving element 20 exceedsthe power supply voltage Vcc, the capacitance and resistance of thelight receiving element 20 for high frequency signals become smallerthan those in the conventional technique. As a result, the opticalreceiver 100 can cope with high-rate communication without dependingupon the power supply voltage Vcc.

FIG. 2 is a schematic diagram showing an optical receiver 100 a as afirst variant of the optical receiver 100. In the optical receiver 100a, the light receiving element row 10 and the light receiving element 20are formed as independent chips. The light receiving element row 10forms an electromotive force device 50 in conjunction with a lightemitting element 30. The light emitting element 30 is supplied withelectric power from the outside, and thereby emits light. The lightreceiving element row 10 is exposed to light emitted from the lightemitting element 30, and generates electric power. The light emittingelement 30 is, for example, an LED or a laser diode or the like. Thelight emitting element 30 may be supplied with electric power by thepower supply voltage Vcc. The light emitting element 30 need not be adevice for transmission.

The light receiving element 20 forms a receiver device 60 in conjunctionwith the amplifier circuit 40.

The optical receiver 100 a has effects similar to those of the opticalreceiver 100. In addition, the light receiving element row 10 and thelight receiving element 20 are independent in the optical receiver 100a. Therefore, the light receiving element row 10 can generate electricpower irrespective of an optical signal S.

FIG. 3 is a schematic diagram showing an optical receiver 100 b as asecond variant of the optical receiver 100. The optical receiver 100 bis different from the optical receiver 100 a in that the light receivingelement row 10 and the light receiving element 20 are integrated on thesame chip. Therefore, the light receiving element row 10 is exposed toan optical signal S together with the light receiving element 20, andthereby generates electric power. In the optical receiver 100 b shown inFIG. 3, the light receiving element row 10 is disposed in a central partof the optical receiver 100 b where the emission of the optical signal Sis the most intensive, and the light receiving element 20 is disposed inits peripheral part. As a result, the light receiving element row 10 cansupply sufficiently great electric power to the light receiving element20. On the other hand, the light receiving element 20 may be disposed inthe central part of the optical receiver 100 b and the light receivingelement row 10 may be disposed in its peripheral part so that the lightreceiving element 20 may receive a signal accurately.

The optical receiver 100 b has effects similar to those of the opticalreceiver 100. In addition, since the light receiving element row 10generates electric power by using the optical signal S in the opticalreceiver 100 b, a light emitting element, which is dedicated to thelight receiving element row 10, is not needed. In addition, since thelight receiving element row 10 and the light receiving element 20 areintegrated on the same chip, the optical receiver 100 b in the presentembodiment can be reduced in size as compared with the optical receiver100 a.

In the optical receiver 100 b, an amplifier circuit 40 may be furtherincorporated on the chip having the light receiving element row 10 andthe light receiving element 20 formed thereon. As a result, the opticalreceiver 100 b can be further reduced in size.

THIRD EMBODIMENT

FIG. 4 is a circuit diagram of an optical receiver 200 according to athird embodiment of the present invention. An optical receiver 200 isdifferent from the first embodiment in that a capacitor 70 connected inparallel with the light receiving element row 10 is further provided.When the electric power supplied from the light receiving element row 10has changed temporarily, the capacitor 70 can compensate for theelectric power change. For example, when irradiation intensity of lightP has become weak temporarily, the capacitor 70 can supply electriccharge to the light receiving element 20 to some degree instead of thelight receiving element row 10. When the irradiation intensity of lightP has increased temporarily, the capacitor 70 can store the electriccharge to some degree instead of the light receiving element row 10. Inother words, the capacitor 70 can smooth noise that has occurred inelectric power supplied from the light receiving element row 10 to thelight receiving element 20. The electric power can be further stabilizedby increasing the capacitance of the capacitor 70.

Although the light receiving element row 10 generates electric power byusing the light P in FIG. 4, the light receiving element row 10 maygenerate electric power by using an optical signal S. Since the opticalsignal S is formed of a high voltage (high) and a low voltage (low),electric power generated by the light receiving element row 10 is nottypically stabilized in this case. However, since the capacitor 70smoothes the optical electromotive force generated from the lightreceiving element row 10, an approximately constant voltage is suppliedto the light receiving element 20.

In addition, in the present embodiment, effects similar to those of thefirst embodiment can be obtained. The capacitor 70 may be formed as achip different from that of the light receiving element row 10 and thelight receiving element 20. For the purpose of reducing the size, thecapacitor 70 may be formed as the same chip as the light receivingelement row 10 or the light receiving element 20. In addition, thecapacitor 70 may be formed as the same chip as both of the lightreceiving element row 10 and the light receiving element 20. As aresult, the optical receiver 200 is further reduced in size. Thecapacitor 70 may be formed as the same chip as the light receivingelement row 10, the light receiving element 20, and the amplifiercircuit 40. As a result, the optical receiver 200 is further reduced insize.

In the embodiments shown in FIGS. 2 to 4, respective connectionrelations of the light receiving element row 10 and the light receivingelement 20 are the same as those in the optical receiver 100 shown inFIG. 1A. However, the respective connection relations of the lightreceiving element row 10 and the light receiving element 20 in theembodiments shown in FIGS. 2 to 4 may be the same as those in theoptical receiver 101 shown in FIG. 1B. In other words, in theembodiments shown in FIGS. 2 to 4, the senses of the light receivingelement row 10 and the light receiving element 20 may be reversed. Inthis case as well, the embodiments shown in FIGS. 2 to 4 have theirrespective effects.

The optical receivers according to the embodiments can cope withhigh-rate communication without being limited in power supply voltage.

Embodiments of an optical transmitter and an optical transceiver willnow be described. In the embodiments of the optical transceiveraccording to the present invention, top surface light of a lightemitting element of surface light emission type is used as an opticalsignal, and its rear surface light is used to expose the light receivingelement row. As a result, the light receiving element row can generateelectric power greater than the power supply voltage.

FOURTH EMBODIMENT

FIG. 6 is a sectional view of an optical transmitter 300 according to afourth embodiment of the present invention. The optical transmitter 300includes a lead frame 110, a light receiving chip 120, and an opticaltransmitter chip 130. The lead frame 110 is formed of a conductivematerial such as metal. The light receiving chip 120 is mounted on thelead frame 110. The optical transmitter chip 130 is mounted on the lightreceiving chip 120.

A light receiving element row 122, which is formed of a plurality oflight receiving elements connected in series, is formed in the lightreceiving chip 120. A light emitting element 132 is formed in theoptical transmitter chip 130 to convert an electric signal to an opticalsignal. The light receiving elements are formed of, for example,photodiodes. In this case, the light receiving element row 122 becomes aphotodiode array. The light emitting element 132 is a light emittingelement of surface light emission type, and it is, for example, an LEDor a VCSEL (Vertical Cavity Surface-Emitting Laser).

A material existing between the light receiving element row 122 and thelight emitting element 132 is transparent to light (light-transparent)so as to transmit light emitted from the light emitting element 132 tothe light receiving element row 122.

The optical transmitter 300 further includes electrodes 124, 125 and134. The electrode 124 is provided between the light receiving chip 120and the optical transmitter chip 130, and connected to one of theelectrodes of the light emitting element 132. The electrode 134 isprovided on the optical transmitter chip 130, and connected to the otherof the electrodes of the light emitting element 132. The electrode 124is connected to a reference potential such as the ground. The electrode134 is connected to, for example, an amplifier circuit (not shown) toamplify an electric signal for transmission. The electrode 125 isprovided on the light receiving chip 120, and connected to one of theelectrodes of the light receiving element row 122. In addition, the leadframe 110 is connected to the other of the electrodes of the lightreceiving element row 122. Furthermore, the lead frame 110 is connectedto the reference potential such as the ground.

FIGS. 7 and 8 are a top view and a bottom view of the light emittingelement 130, respectively. An electrode 134 shown in FIG. 7 covers thesurface of the light emitting element 130 other than an opening part136. The opening part 136 is provided to transmit top surface light P₁emitted from the light emitting element 132. The electrodes 124 shown inFIG. 8 are provided on left and right sides of the rear surface of thelight emitting element 130. A light transmitting part 128 formed betweenthe electrodes 124 is provided to transmit rear surface light P₂ whichis emitted from the light emitting element 132 to the light receivingelement row 122.

Operation of the optical transmitter 300 will now be described.

When an electric signal is input to the electrode 134, a potentialdifference occurs between the electrode 124 and the electrode 134.Because of the potential difference, a forward bias voltage is appliedto the light emitting element 132. Since the light emitting element 132is the surface light emission type, the light emitting element 132 emitslight from its top surface and its bottom surface because of the forwardbias voltage. Top surface light P₁, which is emitted from the topsurface of the light emitting element 132, is transmitted to a lightreceiving element of the other party side via a medium such as space oroptical fiber (not shown) as an optical signal. On the other hand, rearsurface light P₂, which is emitted from the rear surface of the lightemitting element 132, is applied to the light receiving element row 122.

When the light receiving element row 122 is exposed to light, apotential difference is generated between the anode and cathode of thelight receiving element row 122. Since the lead frame 110 is connectedto the ground in the present embodiment, the potential difference, whichis generated by the light receiving element row 122, is output from theelectrode 125 as an output voltage V_(o).

If the signal transmitted from the light emitting element 132 iscomparatively slow in rate, the output voltage V_(o) of the lightreceiving element row 122 depends upon the signal rate. If the signalrate is comparatively fast, however, the output voltage V_(o) becomes agenerally DC voltage. This is because in general, the light receivingelement row has capacitance therein.

In the case where the signal rate is comparatively slow, when acapacitor 140 is connected in parallel with the light receiving elementrow 122 as shown in FIGS. 9 and 10, the output voltage V_(o), which isso stable that it is nearly a DC voltage, can be obtained from the lightreceiving element row 122.

Even in the case where signal transmission is not conducted, the lightemitting element typically transmits a dummy signal such as an idlesignal or a low rate on/off signal. Even in the waiting time duringwhich transmission is not conducted, therefore, the light receivingelement row 122 can output the output voltage V_(o). The use of theoutput voltage V_(o) is not especially restricted. For example, theoutput voltage V_(o) may be used to give a reverse bias voltage to alight receiving element which receives an optical signal as describedlater.

The output voltage V_(o) depends upon the number of light receivingelements 123 which are connected in series in the light receivingelement row 122. Therefore, the output voltage V_(o) can be made greaterthan the power supply voltage by adjusting the number of the lightreceiving elements 123. The light receiving element 123 is, for example,a photodiode. A plurality of the light receiving elements 123 may havedifferent characteristics respectively. Preferably, however, the lightreceiving elements 123 have the same characteristics as each other. As aresult, electric power generated by the light receiving element row 122can be controlled easily by adjusting the number of the light receivingelements 123 connected in series. Furthermore, since a plurality of thelight receiving elements 123 have the same characteristics as eachother, the optical transmitter 300 can be manufactured comparativelyeasily. The characteristics of a light receiving element referred to asherein include an element size, an efficiency of conversion from anoptical signal to an optical current or optical voltage, and parasiticcapacitance.

The optical transmitter 300 according to the present embodiment cansupply a voltage greater than a power supply voltage Vcc supplied fromthe outside (see FIG. 16). The top surface light P₁ of the lightemitting element 132 is used in communication as an optical signal, andits rear surface light P₂ is used to supply electric power. In otherwords, the light emitting element 132 is used for both signaltransmission and electric power supply. As a result, the opticaltransmitter 300 can be reduced in size comparatively.

FIGS. 9 and 10 are equivalent circuit diagrams of the opticaltransmitter 300. With reference to the circuit diagram shown in FIG. 9,the light emitting element 132 emits light according to an electricsignal S_(o) for transmission input from its anode. The light receivingelement row 122 is exposed to the rear surface light P₂ emitted from thelight emitting element 132, and thereby outputs the output voltage V_(o)from its anode. Each of the cathodes of the light receiving element row122 and the light emitting element 132 is connected to the ground incommon.

In the present embodiment, a capacitor 140 is connected in parallel withthe light receiving element row 122. The capacitor 140 is connectedbetween, for example, the electrode 124 and the lead frame 110 shown inFIG. 6. The capacitor 140 may also be provided outside the opticaltransmitter 300. The capacitor 140 may also be parasitic capacitance inthe light receiving chip 120. The output voltage V_(o) is smoothed bythe capacitor 140, therefore, the optical transmitter 300 can output astable output voltage V_(o).

The circuit diagram shown in FIG. 10 differs from the circuit diagramshown in FIG. 9 in that the anode of the light receiving element row 122is connected to the ground and the output voltage V_(o) is output fromthe cathode of the light receiving element row 122. Except for thisdifference, the configuration of the circuit diagram shown in FIG. 10 isthe same as that of the circuit diagram shown in FIG. 9. In each of thecircuit configurations shown in FIGS. 9 and 10, the effects of theoptical transmitter 300 are not lost.

FIFTH EMBODIMENT

FIG. 11 is a sectional view of an optical transmitter 400 according to afifth embodiment of the present invention. The optical transmitter 400differs from the fourth embodiment in that the electrode 124 is providedon the top surface of the optical transmitter chip 130.

FIGS. 12 and 13 are a top view and a bottom view of the opticaltransmitter chip 130 in the optical transmitter 400, respectively. Itwill be appreciated from FIG. 12 that the electrodes 124 and 134 areprovided on the top surface of the optical transmitter chip 130 so as tobe disposed across an opening part 136 from each other. As shown in FIG.13, electrodes are not provided on a bottom surface of the opticaltransmitter chip 130.

Unlike the fourth embodiment, the optical transmitter 400 does not havean electrode between the optical transmitter chip 130 and the lightreceiving chip 120. According to the present embodiment, therefore,electrodes do not intercept the rear surface light P₂. Furthermore, thepresent embodiment is easier than the first embodiment in manufacture.In addition, the present embodiment has effects similar to those of thefourth embodiment.

SIXTH EMBODIMENT

FIG. 14 is a sectional view of an optical transceiver 500 according to asixth embodiment of the present invention. The present embodimentdiffers from the fourth and fifth embodiments in that not only theoptical transmitter but also an optical receiver is provided. In otherwords, it can be said that the present embodiment is an embodimentobtained by applying an optical transmitter according to the fourth orfifth embodiment to an optical receiver.

An optical transmitter 301 may be either of the optical transmitter 300shown in FIG. 6 and the optical transmitter 400 shown in FIG. 11. Avoltage V_(o) output from the optical transmitter 301 is applied to anoptical receiver 302.

The optical receiver 302 includes a lead frame 310 and an opticalreceiver chip 320. Preferably, the lead frame 310 is formed of the samematerial as that of the lead frame 110. The optical receiver chip 320includes a light receiving element 322. The light receiving element 322is, for example, a photodiode. The light receiving element 322 receivesan optical signal P₃, and converts the optical signal P₃ to an electricsignal. Then, the light receiving element 322 outputs the electricsignal via a lead wire 330.

The lead frame 310 is connected to one of the anode and cathodeelectrodes of the light receiving element 322. The lead wire 330 isconnected to the other of the anode and cathode electrodes of the lightreceiving element 322.

A light receiving element row 122 corresponds to the light receivingelement row 10 in the first to third embodiments concerning the opticalreceiver. The light receiving element 322 corresponds to the lightreceiving element 20 in the first to third embodiments.

According to the present embodiment, a lead wire 126 connected to anelectrode 125 in the optical transmitter 301 is connected to the leadframe 310. As a result, the optical transmitter 301 can supply theoutput voltage V_(o) to the light receiving element 322. The lightreceiving element 322 is reverse-biased by the output voltage V_(o), andthe light receiving element 322 can convert an optical signal P₃ to anelectric signal. As described above, the output voltage V_(o) can becomea voltage greater than the external power supply voltage Vcc (see FIG.16). Therefore, the light receiving element 322 can be subjected to areverse bias voltage greater than the external power supply voltage Vcc.As a result, the capacitance and resistance of the light receivingelement 322 for high frequency signals becomes comparatively small, andthe light receiving element 322 can cope with high rate communication.

SEVENTH EMBODIMENT

FIG. 15 is a sectional view of an optical transceiver 600 according to aseventh embodiment of the present invention. The present embodimentdiffers from the sixth embodiment in that the optical transmitter andthe optical receiver are integrated as one body. In the presentembodiment, an optical transmitter chip 130 and an optical receiver chip320 are mounted on a common light receiving chip 120. The lightreceiving chip 120 is mounted on a single lead frame 110. Since theoptical transceiver 600 is mounted on the single lead frame 110, thenumber of components included in the optical transceiver 600 becomessmall.

In the sixth embodiment, one of the electrodes of the light receivingelement 322 is connected to the lead frame 110. In the presentembodiment, however, one of the electrodes of the light receivingelement 322 is connected directly to the electrode 125 to which theoutput voltage V_(o) is output. In the present embodiment, therefore,the output voltage V_(o) can be supplied to the light receiving element322 without being attenuated by resistance of the lead wire 126 or thelike. In addition, the lead wire 126 becomes unnecessary. As a result,bonding of the lead wire 126 also becomes unnecessary. In addition, thepresent embodiment has effects similar to those of the sixth embodiment.

FIG. 16 is an equivalent circuit diagram of the optical transceiver 500or 600 shown in FIG. 14 or 15. A circuit enclosed in a broken line frameC₁ corresponds to the circuit shown in FIG. 9. The anode of the lightemitting element 132 is connected to an output terminal of an amplifiercircuit AMP₁. The cathode of the light emitting element 132 is connectedto the ground. The anode of the light receiving element 322 is connectedto an input terminal of an amplifier circuit AMP₂. The anode of thelight receiving element row 122 is connected to the cathode of the lightreceiving element 322. The cathode of the light receiving element row122 is connected to the ground.

A signal S₁ for transmission is amplified in the amplifier circuit AMP₁,and supplied to the light emitting element 132 as the signal S₀ fortransmission shown in FIG. 9. As a result, the light emitting element132 emits light P₁ and P₂. The light receiving element row 122 receivesthe light P₂, and outputs an output voltage V_(o) greater than theexternal power supply voltage Vcc.

The output voltage V_(o) is applied to the light receiving element 322as the reverse bias voltage. As a result, the light receiving element322 can receive an optical signal P₃, and convert the optical signal P₃to an electric signal. This electric signal is amplified in an amplifiercircuit AMP₂, and output as a signal S₂. In the circuit shown in FIG.16, the output voltage V_(o) is a voltage higher than the ground.

FIG. 17 is an equivalent circuit diagram of the optical transceiver 500or 600 shown in FIG. 14 or 15. A circuit enclosed in a broken line frameC₂ corresponds to the circuit shown in FIG. 10. The anode of the lightemitting element 132 is connected to an output terminal of an amplifiercircuit AMP₁. The cathode of the light emitting element 132 is connectedto the ground. The cathode of the light receiving element 322 isconnected to an input terminal of an amplifier circuit AMP₂. The anodeof the light receiving element row 122 is connected to the ground. Thecathode of the light receiving element row 122 is connected to the anodeof the light receiving element 322.

A signal S₁ for transmission is amplified in the amplifier circuit AMP₁,and supplied to the light emitting element 132 as the signal S_(o) fortransmission shown in FIG. 10. As a result, the light emitting element132 emits light P₁ and P₂. The light receiving element row 122 receivesthe light P₂, and outputs an output voltage V_(o) greater in absolutevalue than the external power supply voltage Vcc.

The output voltage V_(o) is applied to the light receiving element 322as the reverse bias voltage. As a result, the light receiving element322 can receive an optical signal P₃, and convert the optical signal P₃to an electric signal. This electric signal is amplified in an amplifiercircuit AMP₂, and output as a signal S₂.

The circuit shown in FIG. 17 differs from the circuit shown in FIG. 16in that the output voltage V_(o) becomes a voltage lower than theground. Since the ground is connected to the anode of the lightreceiving element row 122, however, a reverse bias voltage is applied tothe light receiving element row 122. In addition, since the outputvoltage V_(o) is greater in absolute value than the external powersupply voltage Vcc, the circuit shown in FIG. 17 can operate in the sameway as the circuit shown in FIG. 16.

In the circuit shown in FIG. 17, a bias obtained by adding the biaspotential of the amplifier circuit AMP₂ and the output voltage V_(o) ofthe light receiving element row 122 is applied to the light receivingelement 322. In other words, in the circuit shown in FIG. 17, a biasgreater than that in the circuit shown in FIG. 16 can be applied to thelight receiving element 322.

In the circuit shown in FIG. 17, the anode of the light receivingelement row 122 is biased to the minus side as compared with the groundpotential. Therefore, the noise and fluctuation of the external powersupply voltage Vcc are hard to affect the output voltage V_(o) of thelight receiving element row 122.

It is desirable that the light emitting element 132, the light receivingelement 322, the light receiving element row 122, the capacitor 140 theamplifier circuit AMP₁ and the amplifier circuit AMP₂ shown in FIGS. 16and 17 are incorporated in the same package. As a result, the opticaltransceiver 300 is reduced in size. Furthermore, the wiring length inthe optical transceiver 300 becomes shorter, and wasteful power becomesunnecessary.

EIGHTH EMBODIMENT

FIG. 18 is a sectional view of an optical transmitter 700 according toan eighth embodiment of the present invention. A light receiving chip120 and an optical transmitter chip 130 are disposed side by side on thesame lead frame 110. The light receiving chip 120 and the opticaltransmitter chip 130 are covered by a transparent resin 150.

In a surface region of the transparent resin 150, a region R₁ throughwhich top surface light P₁ emitted from a light emitting element 132 iscut nearly perpendicularly to the travel direction of the top surfacelight P₁. Thereby, in the top surface light P₁, light going straight oncan pass through the transparent resin 150 without being reflected inthe region R₁.

On the other hand, in the surface region of the transparent resin 150, aperipheral region R₂ of the region R₁ assumes a mirror surface state. Inaddition, the peripheral region R₂ is shaped so as to reflect lightemitted from the light emitting element 132 to the light receivingelement row 122. In the top surface light P₁, light existing around thelight going straight on is reflected by the region R₂ and applied to thelight receiving element row 122. In this way, the top surface light P₁of the light emitting element 132 is not only used as an optical signal,but also a part of the top surface light P₁ is applied to the lightreceiving element row 122. In the present embodiment, both thetransmission of optical signals and the generation of electric power inthe light receiving element row 122 can be achieved by using only thetop surface light P₁ of the light emitting element 132.

Coating may be effected on the surface of the transparent resin 150 inorder to attain the mirror surface state in the region R₂. A reflectormay also be provided outside the optical transmitter 700.

In the optical transmitter according to the present embodiment, avoltage greater than the power supply voltage can be supplied. Theoptical transceiver according to the present embodiment can conducthigh-rate communication without depending upon the power supply voltage.

1. An optical transceiver comprising: a light emitting element toconvert an electric signal to an optical signal and transmit the opticalsignal; a first light receiving element to receive an optical signal andconvert the optical signal to an electric signal, then output theelectric signal; a light receiving element row including a plurality ofsecond light receiving elements connected in series between said lightemitting element and said first light receiving element, said lightreceiving element row being exposed to light emitted from said lightemitting element, and thereby said light receiving element row supplyingelectric power to said first light receiving element; a first amplifiercircuit having an output terminal connected to said light emittingelement, said first amplifier circuit amplifying an electric signal andoutputting the amplified electric signal to said light emitting element;a second amplifier circuit having an input terminal connected to saidfirst light receiving element, said second amplifier circuit amplifyingan electric signal supplied from said first light receiving element andoutputting the amplified electric signal; an anode of said lightemitting element is connected to an output terminal of said firstamplifier circuit; a cathode of said light emitting element is connectedto a reference potential; an anode of said first light receiving elementis connected to an input terminal of said second amplifier circuit; ananode of said light receiving element row is connected to a cathode ofsaid first light receiving element; and a cathode of said lightreceiving element row is connected to the reference potential.